Hammer with hydraulic coupling



Aug. 25, 1970 H. SAUERBREY 3,525,220

HAMMER WITH HYDRAULIC COUPLING Filed Oct. 31, 1968 2 Sheets-Sheet 1 'i n [W 66 65 INVEN TOR.

Bin )D D Q 7 Aug. i970 H. M. SAUERBREY 3,

HAMMER WITH HYDRAULIC COUPLING Filed Oct. 31, 1968 2 Sheets-Sheet 2 IN VEN TOR.

A Tvwe 1ers United States Patent 3,525,220 HAMMER WITH HYDRAULIC COUPLING Horst M. Sauerbrey, Coburg, Germany, assignor to Langenstein & Schemann Aktiengesellschaft, Coburg, Germany, a company of Germany Filed Oct. 31, 1968, Ser. No. 772,266 Claims priority, application Austria, Nov. 6, 1967, A 9,976/67 Int. Cl. FlSb 15/18 US. Cl. 6051 17 Claims ABSTRACT OF THE DISCLOSURE A hammer with a hydraulic coupling in which a drivable tup reciprocates with respect to a mating tup. The driving tup is connected to a drive piston which is supplied with a fluid medium in order to produce a hammer blow, and wherein a drivable tup is hydraulically returnable after a hammer blow.

The present invention relates to a hammer with hydraulic coupling, in which a drivable tup can reciprocate vis-a-vis a mating tup, in a frame, the drivable tup being connected to a drive piston which is supplied with a fluid medium in order to produce a hammer blow, said drivable tup being hydraulically returnable after the hammer blow, in said hammer arrangement there being a passage containing at least one valve device which is closed at the time of the hammer blow, which passage leads out to the exterior from a hydraulic coupling engaging one end of the drivable tup, said hammer arrangement, after the hammer blow, being returned against the force of the driving fluid medium by virtue oftransfer of pressurised fluid into a cylinder and piston arrangement from a fluid supply source, and in said hammer arrangement the fluid supplied by said source being discharged across a valve (the impact or hammer blow valve) which is open for the hammer blow.

One known hammer of this kind, disclosed in German specification 1,116,510, is designed to have a counterblow action, and uses upper and lower tups. In this known double hammer, the drive piston is rigidly connected to the top tup. The fluid supplied to the drive piston in order to produce a hammer blow, is fed into a drive cylinder space. The bottom tup is connected via a hydraulic coupling of feedback type, to the drive piston. The cylinder and piston arrangement, because of the rigid connection between the top tup and the drive piston and because of the presence of the feedback, simultaneously does duty as a hydraulic return mechanism.

In this hammer, the supply of drive fluid is interrupted when the tups are to be returned. However, it is equally possible to maintain the supply of fluid during the return phase and to move the tups back into their initial position against the pressure thereof. This is the case in a hammer discolsed in German Document No. 1,249,637 laid open for inspection, in which the drive fluid is constituted by compressed gas contained in a space surrounding the drive cylinder and locked in when the hammer blow takes place.

The valve device provided in the feedback ararngement in the known hammer introd-uctorily described, serves to fill the feedback arrangement with liquid and keep it filled properly. The pressurised fluid supplied to the cylinder and piston arrangement drives the driveable tup and drive piston back, against the pressure of the drive fluid. When a hammer blow takes place, the pressurised fluid supplied from the source to the cylinder and piston arrangement, flows across the open impact or hammer blow valve, which of course has an adequately lareg area for the purpose, virtually unrestricted. In the case of a hammer of the type described introductorily, bounce eflects at impact must be avoided. Bouncing is the kind of phenomenon in which a tup, after striking a workpiece, in fact springs back away from the workpiece but, after having done so, returns and hits it again, i.e. dances on the workpiece. In order to avoid bounce efliects, in the double hammer disclosed in German Document No. 1,249,637 as laid open for inspection, it is arranged that the pressurised fluid continuously supplied by the source, immediately on impact becomes operative in the cylinder and piston arrangement, by closure of the impact valve, to return the tups.

It will be seen that if the pressure of the drive fluid against which the drive piston is returned, is increased in order to increase the impact energy, then in the case of the double hammer disclosed in German Document No. 1,249,632 as laid open for inspection, bounce effects will not be avoided to an adequate extent. It is the purpose of the invention, considering a hammer of the kind introductorily referred to, to create a new facility for reducing bounce effects. It is a drawback of known double hammers, that they cannot be employed to carry out press work. It is therefore the purpose of the invention to create a hammer of the kind hereinbefore referred to which can also be used for pressing operations. Finally, it is the purpose of the invention to create a hammer of the type hereinbefore referred to, whose drivable tup can easily be moved backwards and forwards without requiring a large amount of, power, and has a low installed height.

In this context, the invention provides a hammer of the kind introductorily referred to which is characterised in that the drive piston is in the form of a free piston; in that the cylinder and piston arrangement engages the free piston; in that a hydraulic return system for the drivable tup is provided; and in that a dump valve is arranged in the passage between the hydraulic coupling linking the drivable tup with the free piston, and an accumulator containing low pressure liquid, the dump valve being open when the tup which is moved to produce the hammer blow, is stationary. The opening of the dump valve is carried out by automatic control, in practice generally about 40 milliseconds after the tup comes to rest.

In the hammer in accordance with the invention, the free piston is not connected rigidly to either of the two tups, but is connected with the drivable tup through the coupling. To produce a hammer blow, the coupling is filled with liquid from the accumulator, and is rendered operative by the closing of the dump valve. On impact, or immediately thereafter, the dump valve is opened so that the pressure of the fluid is collapsed and ceases to act upon the drivable tup, allowing the latter to fly back virtually unrestricted, displacing liquid from the coupling as it does so. The drive piston is returned after the impact, by means of the cylinder and piston arrangement, independently of the drivable tup.

During the normal hydraulic return of the drivable tup and the return of the free piston, i.e. during the phase of winding up the hammer, the dump valve is open and the coupling is filled from the accumulator. The hammer in accordance with the invention in this context exhibits the advantage that the drivable tup or both tups can be retracted apart arbitrarily far without producing any change in the pressure acting upon the retracted free piston. This means that the energy of the hammer blow can be precisely controlled.

The hammer in accordance with the invention can be employed as a press if, additionally, above a press piston engaging the drivable tup, it has a press cylinder space into which pressurised fluid can be introduced via a press line containing a bank of valves, the dump valve then being open both during the extension and retraction movements of the drivable tup. The operation of a hammer of this kind as a press, is carried out in the conventional way using conventional devices. During press operations, the impact valve is closed and the drive piston is stationary. The dump valve is open so that liquid can continuously flow backwards and forwards between the coupling and the accumulator.

As far as the reduction of bounce effects is concerned,

the hammer in accordance with the invention can advantageously be further developed to the extent that the pressure in the fluid supplied by the source to the cylinder and piston arrangement associated with the free piston, is higher than the pressure of the liquid in the hydraulic coupling during the hammer blow, and that the pressure of the liquid in the hydraulic coupling during hammer blow is higher than the pressure of the fluid applied to the free piston. In this hammer, during the hammer blow there prevails in the coupling between free piston and drivable tup a lower pressure than the pressure supplied by the fluid source. This lower pressure, however, allows higher acceleration of the liquid to be achieved and therefore easier discharge of the liquid from the coupling across the dump valve. The hammer in accordance with the invention can be operated as a single hammer in which case, for hammer blow purposes, only the drivable tup is moved and not the mating tup. The hammer in accordance -with the invention, however, will preferably be designed as a double hammer (counterblow hammer), the drivable tup and the mating tup being coupled with one another in the conventional way through a hydraulic feedback arrangement. The feedback arrangement will conveniently be so contrived that it permits of only minimal bounce effects. In this context, the aim is towards using only small quantities of liquid in the feedback arrangement. If the hammer in accordance with the invention is designed as a double hammer, then when press operations are being carried out the feedback arrangement will prefrably be rendered inoperative.

In the hammer in accordance with the invention, the free piston need not be moved when the drivable tup is performing no-load strokes so that a work-performing displacement of the free piston against the pressure of the drive fluid, is avoided. During no-load strokes, the free piston either remains stationary in the lowered position, or, with the impact valve closed, in the retracted position. In this context, it will preferably be arranged that there is connected with a drive cylinder space bounding the free piston, a compression chamber filled with compressed gas as the drive fluid, said chamber being closed off for the hammer blow. Equally, however, it is possible to constantly supply pressurised liquid to the free piston, to serve as drive fluid.

The invention will now be described making reference to the accompanying drawings which illustrate the invention but in no restrictive sense.

FIG. 1 illustrates in section a hammer of double hammer design; and

FIG. 2 illustrates in section the upper part of a single hammer design.

The two hammers illustrated each operate in the vertical attitude and each comprise a bedplate 21, set up on a foundation which has not been shown, said bedplate carrying a frame 18. An upper, drivable tup 1 with an upper die 22, is located opposite a lower tup 16. The tup 16 carries a lower die 23. At the top of the frame, an accumulator 24 is provided.

The embodiment of FIG. 2 is a single hammer design although the devices it exhibits for hammer blow and press functions, can also be employed in a double hammer. The embodiment of FIG. 1 is a double hammer design, the mating tup 16 being coupled with the drivable tup 1 through a hydraulic feedback arrangement 63.

The feedback arrangement 63 has two branches 64 which are disposed laterally of the drivable tup 1 and mating tup 16, in connection therewith. Each arm 64 comprises a coupling rod 12 attached at one end to the drivable tup 1, whose other end does duty as a movable plunger 13. The movable plunger 13 extends into a coupling chamber 14 movable in relation to the mating tup 16, which chamber is filled with liquid, e.g. oil. The coupling chamber 14 is delimited at the top by a piston area or reaction area 15 fixed to the mating tup 16, and at the bottom by a plunger 17 fixed in relation to the bedplate 21. The stationary plunger 17 at the top contains a bore 19 open to the coupling chamber 14, into which bore the movable plunger 13 can he slid. The coupling chambers 14 in both arms 64 communicate with one another through balance line 20 which extend through the .stationary plungers 17.

Each coupling arm 64 is so designed that the coupling chamber 14 extends in the direction of projection of the coupling rod 12, through a component rigidly attached to the mating tup 16. The coupling chamber 14 is closed off at the end opposite to the plunger 13, by the stationary plunger 17, the latter being axially movable in the bore 19 in said component and having one end fixed to the frame 18 whilst its other end is disposed opposite the piston area 15 formed by said component.

In the hammer of FIG. 1, furthermore, a flange 65 is provided at each of the four sides of the mating tup 16', which flange, when said tup is lowered, co-operates with a hydraulic buffer 66 formed in the bedplate 21. On the bedplate 21, beneath the mating tup 16, there is located a known kind of hydraulically operable ejector device 67. Each hammer has a hydraulic return system 3 incorporating a piston 25 which is rigidly attached to the drivable tup 1 through a piston rod 31 and disposed centrally vis-a-vis said tup. This piston 25 delimits the top of a return cylinder space 26 located in the accumulator 24. In the return cylinder space 26, a line 11 opens out. In the embodiment of FIG. 2, this line 11 leads to an accumulator which has not been illustrated. The accumulator is a known kind of device which continuously supplies liquid under relatively low pressure into the line 11 and acts as a spring. In the embodiment of FIG. 1, the line 11 extends via a valve 39 to a main pump 38.

Using the valve 39 located in the line 11 leading to the hydraulic return system 3, the said line 11 can be closed, the valve element being lowered. To this end, a solenoid valve 69 is opened which is located in a control line 68. The solenoid valve 69 is connected via an electrical line 70 to a switch 71 which is located on the frame 18 in the conventional way so that it can be adjusted upwards and downwards. The switch 71 is operable by a dog 72 on the drivable tup 1.

To one side of the return cylinder space 26, projecting partially into the accumulator 24, is a compression chamber 27 which merges into a drive cylinder space 28. A piston 2, in the following referred to as a free piston, can move up and down in the drive cylinder space 28-, the term free piston being used because it is not rigidly connected either to the drivable tup or to the mating tup 16. Thus, it is arranged that the line of movement of the free piston 2 is offset to one side of the line of movement of the piston 25 (of the hydraulic return system 3) rigidly attached to the drivable tup. The compression chamber 27 is closed off for a hammer blow.

The free piston 2 is part of a hydraulic coupling arrangement 6 which links the drivable tup 1 with said free piston. This coupling 6 incorporates aliquid-filled coupling space 29 which includes a space of cylindrical form disposed beneath the free piston 2 and a space communicating therewith and disposed above a piston area 30 fixed rigidly to the drivable tup 1. A plunger component 32 rigidly attached to the frame 18 projects through the piston 25 into the piston rod 31. In the embodiment of FIG. 1, the space above the piston area 30* is located entirely within the piston rod 31 and closed ofl by the plunger component 32. A line leads from the cylindrical space disposed beneath the free piston 2, through the plunger component 32 into the space above the piston area 30. In the embodiment of FIG. -2, the space above the piston area 30 is partially disposed in the piston rod 31 and partially above the piston 25. The plunger component 32 projecting into the piston rod 31 is spaced away from the piston rod.

In both embodiments, it is arranged that the piston rod 31 is attached at one end to the drivable tup 1 and at the other carries the second piston 25 of the hydraulic coupling '6. The plunger component 32 rigidly attached to the frame 18, projects through the piston 25 into the piston rod 31. The coupling space 29 of the coupling arrangement 6, extends along the plunger component 32 to below its free end, into the piston rod 31.

Connected with the coupling arrangement 6 is a dump valve 5, a passage 33 leading from the coupling space 29 into the accumulator 24 and being obturable by the raising of a moving valve element 34 in the dump valve 5. The moving valve element 34 in the dump valve 5 is integral with the moving valve element 35 of an impact or hammer blow valve 8. The impact valve 8 has a large flow area and is disposed in a large-area line which links the cylinder of a cylinder and piston arrangement 4, with the accumulator 24.

A piston 36 of the cylinder and piston arrangement 4, is located beneath the free piston 2 to the top of which the driving fluid is applied, is connected rigidly thereto, and projects out through part of the coupling space 29 in the form of a rod. The free piston 2 also delimits the coupling space 29 of the arrangement 6. Into the cylinder of the cylinder and piston arrangement 4, there leads a pressurised fluid supply line 7, containing a valve 37 and coming from the main pump 38. The pressurised fluid supply line 7 is connected with the line 11 leading to the hydraulic return system 3, via a pressure-relief valve 40. The main pump 38, in the embodiment of FIG. 1, is located in the accumulator 24, and in the embodiment of FIG. 2 is disposed (this is not shown) at the bottom beside the mating tup 16, drawing in fluid from the accumulator 24 via a line 41. The impact valve 8 is located in the accumulator 24 close to the cylinder space of the cylinder and piston arrangement 4. A control line 42 containing a solenoid valve 43, leads from a control pump 44 to the impact valve 8. The control pump 44 feeds liquid from the accumulator 24 through the control line 42 to the impact valve 8. The movable valve element 35 of the impact valve 8 is forced downwards by a weak spring 45, in order to close the valve. The impact valve 8 is designed in the conventional way, so that after being opened by the raising of its valve element 35, it is held open by the dynamic pressure of the fluid flowing out of the cylinder space of the cylinder and piston arrangement 4. It only closes when fluid flow across it ceases. Because the valve elements 34, 35 of impact valve 8 and dump valve 5 are rigidly connected to one another, the impact valve 8 15 coupled with the dump valve 5 in an opposed sense. The dump valve 5, too, because of its connection with the impact valve 8, is controllable by the fluid flowing out of the cylinder and piston arrangement 4 when the drivable tup 1 executes a hammer blow.

The coupling arrangement 6, that is to say its coupling face 29, is communicable via a passage 73 containing a check valve 9, with the accumulator 24 in which the coupling arrangement is located. The check valve 9, in the embodiment of FIG. 1, can be opened and closed from the exterior through the medium of an electrical lead 46-, and in the embodiment of FIG. 2, through the medium of an auxiliary hydraulic arrangement 47. In both cases, the additional provision of the non-return valve 9 operable from the exterior, is made in the passage 73 between the coupling arrangement 6 and the liquid stored in the accumulator 24. Also, it will be apparent from the foregoing that the free piston 2, the cylinder and piston arrangement 4 and the coupling space 6, are located in the accumulator 24 and that the passage. 73 containing the check valve 9, leads into the accumulator.

Each of the two hammers is equipped with a press hydraulic system 10 including a press cylinder space 48 disposed above the drivable tup 1. The press cylinder space 48 is delimited at the bottom end by a press piston area 49 engaging the drivable tup 1 and presented by a piston which can move up and down in the cylinder. In the embodiment of FIG. 1, the piston 25 rigidly attached to the drivable tup 1, presents said area 49, and the press cylinder space 48 surrounds the plunger component 32. In the embodiment of FIG. 2, the press cylinder space 48 is provided in the plunger component 32 and a plunger 50, bearing against the bottom of the piston rod 31, projects upwards into the press cylinder space 48 and there presents the press piston area 49.

Pressurised liquid can be introduced through a press line 51 into the press cylinder space 48. In the embodiment of FIG. 2, a press pump 52 supplies this pressurised fluid via a valve bank 53 using solenoid valves, into the press line 51. The valve bank '53 is adjustable from the exterior, through the medium of an electrical lead 54, so that on the one hand the pressurised liquid flows into the press cylinder space 48 and on the other liquid can flow back out of the press cylinder space into the accumulator 24.

In the embodiment of FIG. 1, the press line 51 leads to a press valve bank 55, which in turn is connected to the main pump 38. The main pump 38 is connected with the pressurised fluid supply line 7 and the line 11, via a return valve bank 56. The assembly of valve bank 55 and valve bank 56, can be operated from the exterior of the accumulator 24, and is designed in the manner usually employed in the case of press functions, with which those skilled in the art will be familiar.

The direction of delivery of the main pump 38 can be reversed in the embodiment of FIG. 1, by means of a lever mechanism 57 and a control hydraulic system 58 mounted on a wall of the accumulator 24. The direction of delivery of the main pump 38 can on the one hand be so adjusted that it co-operates with the press valve bank 55, and on the other so that it co-operates with the return valve bank 56.

In the embodiment of FIG. 1, discharge passages 59 extend between the press cylinder space 48 and the accumulator 24, beneath which passages a poppet valve 60 is located. The poppet valve 61 is rigidly attached to an auxiliary piston 61 which is spring-biased upwards. Above the auxiliary piston 61 there opens out a control line 62 which goes to the main pump 38 when the latter is cooperating with the return valve bank 56.

In the accumulator 24 there is a liquid, e.g. oil, under low pressure. The low pressure is for example in the order of 0 .1 or 0.2 atm. and is at any rate lower than the pressure applied by the drive fluid to the free piston 2, after a hammer blow. The drive fluid, when the free piston 2 has moved back and the hammer is ready to strike, is at a low pressure of for example 40 atm. This low pressure, even when the free piston is moved forward after a hammer blow, is still higher than the low pressure of the liquid in the accumulator.

The drive fluid is a gas, e.g. hydrogen, which is entrapped in the compression chamber 27 and compressed. The low pressure of the gas varies only slightly with movements of the free piston, e.g. by 5 atm.

The coupling 6 and its coupling space 29, can be filled with liquid, e.g. oil. As long as the coupling 6 is open, i.e. is connected to the supply of liquid in the accumulator 24, the aforestated low pressure prevails in the coupling space 29, that is to say the pressure of the liquid in the accumulator. As soon as the coupling 6 is closed and the impact valve 8 is open, a medium pressure develops in the coupling space 29 which is higher than the low pressure and amounts for example to 100 atm.

The pressurised fluid supplied to the cylinder and piston arrangement 4 in order to drive the free piston 2 back, is preferably a liquid, e.g. oil, under high pressure. The high pressure will be higher than the medium pressure and amount, for example, to 200 atm.

In the light of the pressure conditions which have been outlined, it is provided in the case of both embodiments that the piston area 74 on which the drive fluid acts, is greater than the piston area 75 (of the cylinder and piston arrangement 4) upon which the pressurised fluid acts. Thev effective piston area 76 of the coupling 6, which area is connected with the free piston 2, is on the one hand smaller than the effective piston area 74 to which the drive fluid pressure is applied, and on the other hand larger than the effective piston area 75 to which the pressurised fluid is applied. Finally, the piston area 30 (of the coupling 6) connected with the drivable tup 1, can be made smaller than the effective piston area 76 connected to the free piston 2. This means that the travel of the free piston 2 can be kept shorter than that of the drivable tup 1.

In order to carry out forging operations with the ham mer of FIGS. 1 and 2, i.e. to execute a plurality of hammer blows, the compression chamber 27 is filled with compressed gas via known kinds of auxiliary devices (not shown) and closed off. The pressure of the gas on the free piston 2 is operative continually. The main pump 38 continually supplies pressurised liquid through the line 7. In the embodiment of FIG. 1, no pressurised liquid is fed through the press line 51. In the embodiment of FIG. 2, the press pump 52 is switched off. The pressurised liquid coming from the main pump 38 holds the free piston 2 in its uppermost position, against the pressure of the gas in the compression chamber 27. In the embodiment of FIG. 1, the pressurised liquid supplied by the main pump 38 acts via the hydraulic return system 3 t hold the drivable tup 1 in its uppermost, retracted position. In the embodiment of FIG. 2, the drivable tup 1 is held in its retracted position by the accumulator (not shown) via the line 11.

In order to execute a hammer blow, the solenoid valve 43 is briefly operated, so that via the control line 42 the impact valve 8 is lifted and opened against the pressure of the spring 45. With the impact valve 8 open, the cylinder space of the cylinder and piston arrangement 4 is connected with the accumulator 24. In the embodiment of FIG. 1, by opening the impact valve 8 the cylinder space of the hydraulic return system 3 too, can be connected to the accumulator 24. By operating the solenoid valve 43, the dump valve 5 is closed as well. Because the check valve 9 is closed in the case of a hammer blow anyway, the coupling 6 now constitutes a closed system. With the impact valve 8 open and the coupling 6 closed, the gas in the compression chamber 27 drives the free piston 2, and, via the coupling 6, the drivable tup 1, downwards. At the same time, the piston 36 (of the cylinder and piston arrangement 4) attached to the free piston 2, displaces liquid through the impact valve 8 into the accumulator 24. The movable valve element 35 of the impact valve 8 is held open during this time, by the flow of liquid passing across it. It drops as soon as the drivable tup 1 ceases its downward movement at impact, and the flow of liquid ceases. With the dropping of the valve element 35, in the impact valve 8, the dump valve 5 is opened and the coupling space 29 of the coupling 6 is connected to the accumulator 24.

The tup 1, springing back after impact, is thus relieved of the gas pressure and can fly back freely and be moved back properly by the liquid flowing into the cylinder of the hydraulic return system 3. At the same time, pressurised liquid delivered by the main pump 38 is fed into the cylinder and piston arrangement 4, and drives the free piston 2 back.

For pressing operations, the free piston 2 will preferably remain in its extended position and is held there when the impact valve 8 is closed and by reason of the position of the one-way valve 37. The hammer is then operated in the manner of a normal press, the dump valve 5 being open because the impact valve 8 is closed, and the coupling space 29 being in communication with the accumulator 24. In the embodiment of FIG. 1, the main pump 38 is alternatively set to feed into the press cylinder space 48, via the press valve bank 55, to produce extension of the drivable tup 1, and then the return valve bank 36 is set to feed into the cylinder space of the hydraulic return arrangement 3 in order to return the drivable tup. In the embodiment of FIG. 2 on the other hand, the main pump is switched ofi and the press pump 52 is used to supply fluid into the press cylinder space 48, to make the drivable tup I extend. This supply is interrupted in order to return the drivable tup, the tup being moved back by the accumulator which has not been shown.

I claim:

1. A hydraulic hammer comprising a drivable tup and a cooperating mating tup, a hydraulic return system operatively connected to the drivable tup, a free drive piston disposed in a chamber, a piston disposed in a piston and cylinder unit connected to the free piston, a hydraulic coupling operably relating the said chamber to the hy draulic return system, the hydraulic coupling including a first valve connecting the said chamber to a low pressure fluid, and a second valve connected to the cylinder of the cylinder and piston unit for maintaining the pressure in the said cylinder when the pistons are in a first position whereby upon actuation of both the valves the pistons are moved to respective second positions to thereby activate the hydraulic return system and in turn the drivable tup in a retraction stroke.

2. The hydraulic hammer as claimed in claim 1, wherein the first valve is a dump valve and the second valve is an impact valve and the said valves connected t operate cooperatively.

3. The hydraulic hammer as claimed in claim 1, wherein the free drive piston and chamber includes a compression chamber for moving the piston from its first to its second position.

4. The hydraulic hammer as claimed in claim 3, wherein the cylinder of the cylinder and piston unit receives the piston of the unit in its second position and is adapted to contain fluid for maintaining the piston in its first position in opposition to the force exerted by the compression chamber.

5. The hydraulic hammer as claimed in claim 2, wherein the impact valve is connected between the cylinder in the cylinder and piston unit and a source of fluid pressure and in its opened position permits the flow of fluid into the cylinder to return the piston to its first position.

6. The hydraulic hammer as claimed in claim 1, wherein the hydraulic return system includes a fixed plunger component and a piston rod slidably mounted thereon, one end of the piston rod being connected t the driveable tup for movement therewith and the other end to a piston.

7. The hydraulic hammer as claimed in claim 2, wherein the closure of the dump valve makes the hy draulic coupling a closed fluid circuit between the cylinder and piston unit and the hydraulic return system.

8. The hydraulic hammer as claimed in claim 6, wherein the area located between the piston and a portion of plunger component is adapted to receive pressurized fluid which is supplied via a press line containing a plurality of valves.

9. The hydraulic hammer as claimed in claim 1 wherein pressurised fluid is supplied from the pressure source via a source line so that the pressure in the cylinder and piston unit when engaging the piston is higher than the pressure of the fluid in the hydraulic coupling at the time of a hammer blow, and the pressure of the fluid in the hydraulic coupling at said time is higher than the pressure of the drive fluid applied to the free piston.

10. The hydraulic hammer as claimed in claim 6, wherein a variable space is formed by the piston, the piston rod and the plunger component into which fluid flows to return the hydraulic return system to its initial position.

11. The hydraulic hammer as claimed in claim 10, wherein a line leading from variable space of the hydraulic return system to the source of fluid pressure includes a solenoid operable valve operable by a switch which is operated by a dog carried by the drivable tup.

12. The hydraulic hammer as claimed in claim 1, wherein an externally operable check valve is arranged in a channel between the hydraulic coupling and a liquid reserve.

13. The hydraulic hammer as claimed in claim 12, wherein the piston of the cylinder and piston unit and the hydraulic coupling are arranged in an accumulator, and the channel containing the check valve opens into the accumulator.

14. The hydraulic hammer as claimed in claim 1, wherein the path of movement of the free piston is oflset from the path of movement of the piston of the hydraulic return system which is rigidly connected to the drivable tup.

15. The hydraulic hammer as claimed in claim 6, wherein the coupling space of the hydraulic coupling extends along the plunger section to a point below its free end in the piston rod.

16. The hydraulic hammer as claimed in claim 1, wherein the drivable tup and the mating tup are connected to one another through a hydraulic feedback arrangement, one tup carrying a coupling rod which penetrates into a liquid-filled coupling space formed by a piston area in the other tup and the latter being reciprocably movable.

17. The hydraulic hammer as claimed in claim 16, wherein the coupling space is closed off by a stationary plunger having a bore in which the coupling rod is adapted to be received, one end of the stationary plunger is fixed and its other end is located opposite the said piston area.

References Cited UNITED STATES PATENTS 2,403,912 7/1946 Doll. 2,455,747 12/ 1948 Fischer et al 60-51 2,877,624 3/1959 Zoller 6051 EDGAR W. GEOGHEGAN, Primary Examiner US. Cl. X.R. 60-52 

